Draft Lane Cove Southern Catchments Flood Study

A flood study investigates how flooding behaves in an area in storms ranging from common to very rare. It shows where water is likely to travel, how deep and fast it may get, and which properties, roads, and other infrastructure could be affected.

About 5.7 square kilometres of creek catchments that drain to the Lane Cove River south of the Pacific Highway:  Sugarbag Creek, Little Blue Gum Creek and Blue Gum Creek. These waterways are in the suburbs of Killara, Lindfield and Roseville. 

Council engaged flood engineers WMAwater to carry out the study. The cost was shared between Council and the NSW Government, through the Department of Climate Change, Energy, the Environment and Water’s Floodplain Management Program.

It's the first step in managing flood risk in the area. It also gives Council, the SES and residents a shared understanding of flood behaviour, to guide planning and emergency response.

Search your address on Ku-ring-gai Maps, Council's online mapping tool. To view flooding information, select “Hydrology” from the “Layers” menu. If the study shows your property may be affected, Council will also send you a letter or email in the first week of exhibition.

AEP stands for Annual Exceedance Probability. It's the chance of a flood that size happening in any one year. A 1% AEP flood has a 1 in 100 chance of happening in any year (once commonly called a "1 in 100 year flood"). A 0.2% AEP flood is rarer, about a 1 in 500 chance, but it can still happen, and rare floods can occur close together.

PMF stands for Probable Maximum Flood. It's the largest flood considered possible in this catchment. It's used mainly for emergency planning, and it also affects some development rules on land beyond the areas that flood more often.

The Flood Planning Area (FPA) is land that may be affected by flooding during a major flood event. In Ku-ring-gai, it includes areas expected to flood in a 1% annual chance flood, plus an extra safety margin called a freeboard.

There are two types of flood risk included within the FPA: mainstream flooding (from creeks and waterways) and overland flooding (from stormwater flowing over the ground). Properties within the FPA are subject to flood-related building and development rules to help reduce flood risk and ensure new development is safe and suitable for the area.

Having FPA identified on your property does not necessarily mean it floods regularly, or that it has ever flooded. It means that flood modelling has indicated there is a level of flood risk that be must considered when assessing development and land use.

The Probable Maximum Flood (PMF) Tagging Area is land that may be affected by flooding during a credible worst-case flood. The PMF Tagging Area includes the outer limit of where flood waters are likely to reach.

While this does not mean the property is expected to flood during ordinary storms or typical flood events, it indicates there is a potential flood risk in the most severe flooding circumstances.

Having PMF Tagging Area identified on your property does not necessarily mean it floods regularly, or that it has ever flooded. This information is used to support emergency planning and to assess flood risk when considering future development for critical facilities such as seniors living and early education and care facilities.

Two models were used together. The first, DRAINS, estimates how much rainfall turns into runoff. The second, TUFLOW, is a two-dimensional model of the ground surface. It simulates how that runoff actually moves across the land and through gutters, pipes, culverts and creeks.

Yes. There are no stream gauges in the catchment to measure past flood levels directly, so the model was tested against three real storms, from 2018, 2022 and 2024, and compared with what residents reported. It matched what people actually experienced fairly closely, usually within about 20 centimetres.

Yes. In mid-2024, Council ran a survey and received 69 responses, 47 from residents who had experienced flooding before. About 80 of these responses, along with resident photos, were used to check the model against what actually happened.

Yes. Storms are expected to become more intense as the climate warms, so the study tested what would happen if rainfall was as intense as today's rarer events. Under this test, flood levels in the creeks could rise by roughly 5 to 30 centimetres.

It might. Council and private certifiers use flood mapping like this to set flood-related building rules, such as minimum floor heights, for affected properties. Once the study is finalised, it will help guide these rules.

It can, for some types of development. Uses that need extra care for vulnerable people, or that involve hazardous storage or industrial establishments, can still face flood-related conditions even in areas that only flood in the most extreme events.

From 31 August to 16 October 2026. Written submissions must be received by midnight on 16 October 2026.

Quote reference number S13084-1. You can submit online through Council's Your Say page, by email to krg@krg.nsw.gov.au, or by post to the Manager, Governance and Corporate Strategy, Ku-ring-gai Council, Locked Bag 1006, Gordon NSW 2072

Flood study appointments are on Tuesday 22 September at West Pymble Community Hall, Thursday 24 September at West Lindfield Community Hall and Thursday 1 October at Ku-ring-gai Town Hall, Pymble.

Details on booking a flood study appointment are available on this page.

Council will review all submissions and update the study where needed. A summary of the feedback, along with the revised study, will then go to Council for a decision. Once Council adopts the final flood mapping, Section 10.7 planning certificates will be updated. For all properties identified as being within either the Flood Planning Area or Probable Maximum Flood tagging area this is noted within the planning certificate.